stream/iter: fromSync() rejects dual sync/async iterables instead of using Symbol.iterator

### Version main ### Platform ```text macOS 26.5.0 ``` ### Subsystem stream ### What steps will reproduce the bug? ```js import { fromSync, textSync } from 'node:stream/iter'; const input = { *[Symbol.iterator]() { yield new TextEncoder().encode('sync'); }, async *[Symbol.asyncIterator]() { yield new TextEncoder().encode('async'); }, }; try { console.log(textSync(fromSync(input))); } catch (err) { console.log(`${err.name}: ${err.message}`); } ``` ### How often does it reproduce? Is there a required condition? Always ### What is the expected behavior? Why is that the expected behavior? ```console sync ``` `fromSync()` currently rejects any object with `Symbol.asyncIterator` before checking for `Symbol.iterator`. Per Spec [§8.2](https://stream-iter.jasnell.me/#fromsync-method), only async-only inputs should be rejected here; a dual sync+async iterable should be accepted through its synchronous iterator. ### What do you see instead? ```console TypeError: The "input" argument must be an a synchronous input (not AsyncIterable). Received an instance of Object ``` ### Additional information _No response_